FIG. 1 illustrates a conventional polarizing beam splitter (“PBS”) 100. PBS 100 is made of a polarizing film 105 disposed between two glass prisms 110 and 115. Polarizing film 105 is engineered to achieve the desired polarizing effect whereby the majority of S polarized light is reflected while the majority of P polarized light is transmitted.
The two halves of PBS 100, or prisms 110 and 115, are fabricated of glass due to the constraints of fabricating polarizing film 105. Fabricating the multi-layer film requires repetitious, high temperature manufacturing processes. Glass is a transparent material that is capable of withstanding these repetitious, high temperature processes without degrading its desirable optical properties.
Glass is not anisotropic, which is to say it does not induce birefringence. Birefringence within a material volume imparts a different index of refraction to different axes of polarization. In optical systems, birefringence can be detrimental to the image quality, since it can decompose a single ray of light into multiple divergent rays light. For example, many optical grade plastics are birefringent and the degree of birefringence can increase with heat exposure. Heat exposure within plastics can induce localized stresses within the material bulk. These localized stresses in turn can result in deleterious birefringence. In optical systems that are polarization sensitive, the birefringence can particularly degrade the quality of the optical system.